Tiered Risk Assessment for Petroleum Hydrocarbons C6–C9: A Case Study at a Typical Decommissioned Petroleum Refinery Site in Gansu Province

No method to assess the risks of petroleum hydrocarbon pollutants C6–C9 in soils on construction land in China has been established. At one decommissioned petroleum refinery site in northwestern China, we performed an innovative tier 3 risk assessment method using carbon fraction proportions. Using HJ 25.3 guidelines, the risk-screening value for soil contamination of land by petroleum hydrocarbons was 192 mg kg−1 for industrial land use. However, based on site-specific parameters, this value was 226 mg kg−1, with a corresponding contaminated soil volume of 381,904 m3. A tier 3 risk assessment incorporating carbon fraction proportions and site-specific parameters yielded a risk control value of 2370 mg kg−1 and reduced the soil volume requiring decontamination to 87,047 m3, potentially saving CNY 324 million (~USD 45.5 million as of November 2025) in remediation costs. Therefore, implementing a tier 3 risk assessment for C6–C9 pollutants can optimize remediation strategies and enhance the precision and scientific rigor of petroleum hydrocarbon-contaminated soil remediation.